1. Field of the Invention
The present invention relates to a process for preparing photoconductive particles, and more particularly, to a process for preparing photoconductive particles having a water insoluble precipitate on the surface thereof which are prepared by the use of ion exchange resins containing the desired anion, in a process for preparing photoconductive particles which have less forming ghost image or excellent reproducibility in half tone by deposition of a water insoluble metal compound on the surface of the photoconductive particles.
2. Description of the Prior Art
Photoconductive particles are dispersed into a binder, and a photoconductive layer is formed by the resulting mixture. An electrophotographic photosensitive member comprising the photoconductive layer is used, and the characteristics of the photosensitive member depend upon the dispersing condition of the photoconductive particles in the binder, particularly, depending upon the characteristics of the photoconductive particle itself.
Generally, in the case of a photosensitive member using photoconductive particles, contrast of electrostatic images tends to decrease in a high humidity atmosphere. In short, the photoconductive member is not of good humidity resistance. Further, at a high speed copying by an electrophotographic process, it is required that an electrostatic image is formed immediately after an electrostatic image produced in the preceding cycle has disappeared. At this time, it is necessary that the preceding image is eliminated quickly and completely. However, sometimes an image which has not been completely eliminated is overlapping on an electrostatic image to be subsequently formed. In short, a ghost image is formed sometimes.
In the techniques of electrophotographic photosensitive members, the maximum value of the ratio of the change in surface potential (.DELTA.V) to the change of exposure E (hereinafter represented by .DELTA. log E) is very important. This maximum value is called .gamma..multidot.value. The above-mentioned relation is represented by the following formula. ##EQU1##
The .gamma. value has a great effect on the reproducibility of original information during latent image formation in an electrophotographic processes. That is, where .gamma. value of a photosensitive member is very high, the resulting latent images are very unstable since the surface potential is very sensitive to even a minor change of exposure and, in particular, latent images corresponding to a light of intermediate intensity are so unstable that the developed images can not contain any half tone (grey) and are of low gradation. On the contrary, where .gamma. value is too small, fog is formed and good images can not be obtained.
Therefore, it is desired that photoconductive particles having the desired .gamma. value are prepared so as to reproduce half tone satisfactorily.
It is effective for improving humidity resistance, inhibition of ghost image, and reproducibility of half tone that a water insoluble metal compound is deposited on the surface of photoconductive particles as proposed in Japanese Patent Application Nos. 121288/1979 and 121504/1979.
A method of depositing a water insoluble compound on the surface of photoconductive particles according to the two Japanese Patent Applications comprises the addition of water-soluble sulfides, hydroxides, carbonates, or the like to a mixture including the photoconductive particles in an aqueous solution of water-soluble metal salt with stirring, whereby the water-soluble metal salt reacts with the water-soluble sulfides, hydroxides, or carbonates etc., and deposits the resulting water insoluble metal compound on the surface of the particles. However, in this method, water-soluble materials comprising counter ions corresponding to the above-mentioned water insoluble compounds remain in the resulting mixture. Consequently, unnecessary water-soluble materials should be further removed by procedures such as washing with water.